New green chemical techniques in textile coloration processes Dr. Richard S. Blackburn Senior Lecturer and Head of Green Chemistry Group Centre for Technical Textiles UNIVERSITY OF LEEDS, LS2 9JT, UK r.s.blackburn@leeds.ac.uk

Where can Green Chemistry have an impact in Coloration? Dye chemistry Alternative synthesis, sustainable source, natural platform chemicals Dyes in effluent Reduction (efficiencies of sorption) and cleaner treatment technologies Auxiliary chemicals Reduction in use and emission of harmful auxiliaries (e.g. salt, reducing agents, carriers) Application processes Reduction in energy, water usage, time Coloration of ‘greener’ fibres PLA, PHAs, lyocell, etc. © University of Leeds 2006

Sustainable platform chemicals Natural dyes derived from plant material represent a more sustainable source of colorants Natural dyes colour natural fibres (cotton, wool, silk) to a greater or lesser extent need application with a mordant (salts of Cr, Sn, Zn, Cu, Al, Fe) to secure sufficient wash and light fastness and to give good build-up Natural dyes have found limited success in coloration of synthetic fibres PET has a 45% share of the global textile market Madder plant (Rubia tinctorum L.) is an important dye plant produces the dye alizarin (1,2-dihydroxyanthraquinone) also contains rubiadin (1,3-dihydroxy-2-methylanthraquinone) and purpurin (1,2,4-trihydroxyanthraquinone) © University of Leeds 2006

Sustainable platform chemicals Derivatisation of alizarin to produce more hydrophobic molecule higher affinity for hydrophobic polyesters Successful synthesis of 1-hydroxy-2-ethylanthraquinone (1H2EA) 93% yield confirmed by FT-IR and NMR OH at 1-position not derivatised due to intramolecular hydrogen bond formation and lower intrinsic reactivity © University of Leeds 2006

Sustainable platform chemicals Problem with application of alizarin is pH sensitivity 1H2EA displays no such sensitivity due to derivatisation of 2-OH Table: The effect of pH on solubility and colour of alizarin and 1H2EA pH Alizarin 1H2EA 4 v. sparingly soluble no colour insoluble 7 sparingly soluble orange/yellow colour 10 soluble purple colour © University of Leeds 2006

Sustainable platform chemicals Dyes applied with dispersing agent to PET and PLA Colour strength (K/S) achieved with 1H2EA higher than alizarin Dyeings unlevel, poor quality with alizarin Dyeings level, bright, good quality with 1H2EA Alizarin gives higher K/S on PET w.r.t. PLA, but opposite observed for 1H2EA increased interactions with PLA via alkyl chain addition Table: Colour strength (K/S) values of dyed samples Conditions of application Alizarin 1H2EA PET PLA 1% omf at 90 °C   1.5 4.3 1% omf at 100 °C 3.1 2.1 5.1 1% omf at 130 °C 6.5 8.7 4% omf at 115 °C 2.2 10.6 4% omf at 130 °C 19.2 20.9 © University of Leeds 2006

Sustainable platform chemicals Wash fastness comparable and excellent on all dyeings Light fastness considerably higher for 1H2EA compared to alizarin 2-OH susceptible to photo-oxidation, as it cannot form an intra-molecular H-bond In 1H2EA 2-OH derivatised, so not as susceptible to photo-oxidation Table: Light fastness of dyed samples (1-8 scale) Conditions of application Alizarin 1H2EA PET PLA 1% omf at 90 °C   3 5 1% omf at 100 °C 6 5/6 1% omf at 130 °C 4 4% omf at 115 °C 3/4 4% omf at 130 °C © University of Leeds 2006

Green Chemistry Sulphur Dyeing Economical, good colour strength, good fastness dyeings on cellulosics Significant share of the colorants market annual consumption of ca. 70,000 tons C. I. Sulphur Black 1 alone represents a substantial portion (20-25%) of dyestuff market for cotton highest consumption of any single textile dye in the world Complex mixtures of reproducible, but uncertain, compositions Contain within their ring structure thiazole, thiazone, or thianthrene as chromophores All sulphur dye molecules contain disulfide linkages © University of Leeds 2006

Mechanism of sulphur dyeing Initially dye is in insoluble oxidised (pigment) form Addition of reducing agent cleaves a proportion of the disulfide linkages to form the partially soluble ‘leuco’ sulphur form Further addition of reducing agent and increase in redox potential causes reduction of the remaining disulfide linkages and quinoneimine groups After exhaustion of the dye onto fibre, the reduced, adsorbed dye is reformed in situ within the fibre by air or chemical oxidation © University of Leeds 2006

Reducing agents in sulphur dyeing Sulphur dyes themselves have a relatively low detrimental environmental impact free from heavy metals and AOX Significant environmental problem with the dyeing process employ sulfides as reducing agents 90% of all sulphur dyes are reduced using sodium sulfide Discharge of sulfides only permissible in very small amounts (usually the legal allowance is 2 ppm) danger to life from liberated hydrogen sulfide corrosion of sewerage systems damage to treatment works high pH aquatic life down stream significantly affected damage to the DNA of tadpoles classed as micropollutants over time the substance can reach high concentrations © University of Leeds 2006

Alternative reducing agents Thiourea dioxide from both a practical and ecological point of view dyeings comparable, but environmental effect unclear significantly more expensive than sodium sulfides Indirect cathodic reduction processes successfully reduce sulphur dyes some reducing agent was required to prevent premature re-oxidation of the dye dyeing was comparable electrolysis is an appreciably more expensive technology Glucose/NaOH above 90°C has sufficient reducing potential no current systems in commercial use dyeings secured had lower colour strength and fastness no fundamental work on the reducing sugar/NaOH system conducted to understand optimum © University of Leeds 2006

Application of various reducing D-sugars D-arabinose D(-)-fructose D(+)-galactose α-D-glucose β-D-lactose D-maltose sodium polysulfide sodium hydrosulfide Blackburn, R. S.; Harvey, A. Env. Sci. Technol. 2004, 38 (14), 4034. © University of Leeds 2006

D-arabinose D(-)-fructose D(+)-galactose α-D-glucose

β-D-lactose D-maltose

Environmental and economical considerations Relative theoretical COD and price of reducing agents per kg dyed cotton Reducing agent g O2 kg-1 dyed cottona £ kg-1 dyed cottona sodium sulfide 51.3 1.60 sodium hydrosulfide 71.3 1.18 D-arabinose 66.6 28.06 D(-)-fructose 1.65 D(+)-galactose 4.14 α-D-glucose 0.58 β-D-lactose 70.1 2.08 D-maltose 4.30 a Based on 2.5 g dm-3 reducing agent (typical optimum concentration) at a liquor ratio of 25:1 © University of Leeds 2006

Greener reactive dyeing of cellulose Treatment of cellulose with cationic, nucleophilic polymers to enable reactive dyeing at neutral pH without electrolyte addition Reactive dyeing problems High electrolyte concentrations used High colour concentrations in effluent High volume of water consumed © University of Leeds 2006

Problems with high electrolyte concentration High levels of salt (sodium sulfate/chloride) used when dyeing cotton Particularly reactive dyes Fibre has negative charge in water Repels anionic dyes – low adsorption Electrolyte screens negative charge Overcomes repulsion between dye anions and negative fibre surface to allow adsorption Soil too alkaline to support crops Kills aquatic life Examples of fresh water courses turned saline downstream from reactive dyeing operations Difficult to remove from effluent © University of Leeds 2006

Mechanism of reactive dye fixation to cellulose (Nucleophilic substitution)

Mechanism of reactive dye fixation to cellulose (Michael Addition)

Colour (unfixed dye) in effluent Reactive dyes poor fixation 10-40% dyestuff hydrolysed Goes down drain Aesthetically unpleasant Blocks sunlight Algae overpopulate Reduction in O2 levels in water Suffocation of flora and fauna in watercourses Clean effluent High cost © University of Leeds 2006

High water consumption High level of water used in reactive dyeing Incredible volume used in wash-off of hydrolysed dye Up to 10 separate rinsings High energy consumption 50% total cost dyeing procedure © University of Leeds 2006

Pre-treatment agents Copolymer of diallyldimethylammonium chloride and 3-aminoprop-1-ene (PT1) Copolymer of 4-vinylpyridine quaternised with 1-amino-2-chloroethane (PT2) © University of Leeds 2006

High substantivity of pre-treatments for cotton Both pre-treatment polymers are highly substantive to cellulosic fibre ion-ion interactions between cationic groups in the agent and the anionic carboxylic acid groups in the substrate low pKa values will be ionised at the pH values of application (pH 6-7) Other forces of attraction H-bonding, van der Waals © University of Leeds 2006

Conformational interaction between PT1 Conformational interaction between PT1 and cellulose © University of Leeds 2006

PT2 Ion-dipole interactions between cellulose hydroxyl groups and pyridinium residues of PT2 Yoshida H-bonding between cellulose hydroxyl groups and pyridine residues in PT2 © University of Leeds 2006

Mechanism of operation (schematic) © University of Leeds 2006

Advantages of pre-treatment system Polymers cationic No requirement for salt Nucleophiles in polymer more reactive than hydroxyl groups in fibre Neutral pH of application Hydrolysis minimised Colour fixation yield maximised Less colour in effluent Less wash-off requirement Significant reduction in operation time Significant reduction in water consumption © University of Leeds 2006

System comparison Procedure Wash-off stages Time (mins) Water (ℓ/kg fabric) NaCl (g/kg fabric) Na2SO4 (g/kg fabric) Na2CO3 (g/kg fabric) Other Chemicals (g/kg fabric) Remazol RR 6 355 145 1250 500 acetic acid (60), detergent (20) Procion H-EXL 4 365 105 1625 detergent (20) Cibacron F 5 295 125 1500 Pre-treatment 1 195 50 pre-treatment (10), detergent (20)

Publications Blackburn, R. S.; Burkinshaw, S. M. Green Chemistry 2002 4 (1), 47. Blackburn, R. S.; Burkinshaw, S. M. Green Chemistry 2002, 4 (3), 261. Blackburn, R. S.; Burkinshaw, S. M. Journal of Applied Polymer Science, 2003, 89, 1026-1031. “Dye Hard”, New Scientist, 1st December 2001 “Greener Dyes”, The Alchemist, 6th February 2002 “Problem Fixed”, Chemistry in Britain, April 2002 © University of Leeds 2006

DyeCat Ltd. A University of Leeds Spinout Company Dr. Patrick McGowan Organometallic chemistry Novel polymerisation catalysts Organometallic anticancer drugs Dr. Richard Blackburn Coloration of natural and synthetic polymers and fibres Physical organic chemistry of dyeing processes Green Chemistry in the textile and coloration industries Prof. Chris Rayner Organic synthesis (pharmaceuticals and fine chemicals) Supercritical carbon dioxide Green Chemistry ©DyeCat 2006 © University of Leeds 2006

DyeCat Technology Patented technology for the preparation of light absorbing polymeric materials (IR, visible, UV). Variety of approaches; allows flexibility in Polymer composition Polymer molecular weights and polydispersities Coloration strength Range of light absorbing chromophores Applicable to natural and synthetic polymers (particularly polyesters such as PLA and PET). Superior coloration technology Homogeneous colorant throughout cross section of polymer Increased wash and light fastness Greatly improved preparative method Significant cost reductions on comparable conventional technology Reduced environmental impact Applicable to sustainable, biodegradable polymers such as PLA and PHB. ©DyeCat 2006 © University of Leeds 2006

Contacts Laura Bond (general inquiries) Dr. Patrick McGowan Laura@techtrangroup.com Dr. Patrick McGowan p.c.mcgowan@leeds.ac.uk Dr. Richard Blackburn r.s.blackburn@leeds.ac.uk Prof. Chris Rayner c.m.rayner@leeds.ac.uk www.dyecat.com ©DyeCat 2006 © University of Leeds 2006

Acknowledgements Colleagues Research Assistants PhD Students Prof. Chris Rayner Prof. Tony Clifford Prof. Stephen Burkinshaw Prof. Carl Lawrence Prof. Paul Knox Dr. Patrick McGowan Dr. Steve Russell Dr. Abbas Dehghani Research Assistants Dr. Tony Blake Dr. Nagitha Wijayathunga Dr. Xiangfeng Zhao PhD Students Iram Abdullah Nabeel Amin Ioannis Drivas Parikshit Goswami Anna Harvey Andrew Hewitt Nandan Kumar Wei Zhang Industrial Partners Body Shop International plc (UK) DyStar (Germany) Lenzing Fibers Ltd. (Austria) NatureWorks LLC (USA) Reilly Industries inc. (USA) Uniqema (UK) © University of Leeds 2006